This invention relates to segmented pipe couplings, such couplings being comprised of two or more arcuate coupling segments having bolting pads at their respective ends enabling the coupling segments to be bolted to each other in encircling relation with a pipe or a fitting, the segmented pipe coupling being employed to connect adjacent ends of pipes to each other, or, to connect a fitting to a pipe, or to another fitting.
While not limited thereto, the present invention finds particular application in segmented pipe couplings that are employed to interconnect lengths of high-density polyurethane pipe, the present invention also finding application in segmented pipe couplings employed for interconnecting lengths of cut or roll grooved metal pipe, in which it is intended that the keys of the coupling segments engage the bottom wall of the groove throughout the entire arcuate extent of the respective coupling segments.
Segmented pipe couplings are well-known in the art, including segmented pipe couplings having teeth extending circumferentially of the inner periphery thereof for biting and gripping engagement with the outer surface of a pipe.
The usual manner of securing the coupling segments to one another is by the use of traction bolts, which extend through apertures in adjacent bolting pads of a pair of coupling segments, the traction bolts having a head at one end that engages a bolting face of the associated bolting pad, the bolting face extending on a radius of the coupling segment, and either parallel to, or at an angle to a radial plane that includes the longitudinal axis of the coupling segment.
The other end of the traction bolt is threaded, for it to receive a nut, which similarly engages the associated bolting face of the next adjacent coupling segment, that bolting face extending either parallel to the bolting face of the next adjacent coupling segment, or, extending at an angle thereto, for the respective bolting faces to diverge and to define and include angle, and be other than truly parallel to one another.
Commonly bolt holes are provided in the bolting pads for the reception of a shank of the traction bolt, the shank of the traction bolt being inserted through the bolt holes in the adjacent bolting pads, subsequent to which the nut is applied to the shank of the traction bolt, and, the nut is then torqued down to draw the bolting pads of the respective coupling segments towards each other, and, in turn, to draw the assembled segmented pipe coupling into clamping engagement with the exterior of the associated pipes or fittings.
The coupling segments, while essentially being rigid, are capable of flexure to a limited extent in a direction to reduce the arcuate radius of the coupling segment, and, permit the coupling segment to extend in continuous engagement with the outer surface of the associated pipe or fitting.
This flexing movement is of particular value in segmented pipe couplings employed for interconnecting lengths of high-density polyurethane pipe [HDPE], the coupling segments being provided with teeth on their inner periphery which are to bite into the outer surface of the pipe, and thus anchor the segmented pipe coupling against movement axially of the associated pipe.
This capability of flexing of the coupling segments is employed to advantage in segmented pipe couplings that incorporate only two coupling segments, which each subtend an arc of a semi-circle. Provision must be made for positioning the internal teeth of the coupling segments over the pipe periphery prior to torquing down of the traction bolts, i.e., the radially inner surfaces of the teeth at the ends of the coupling segments must be spaced radially outwardly of the axis of the coupling segment by a distance that is equal to the radius of the outer surface of the pipe, in order to permit the coupling segment to be assembled over the pipe periphery. On torquing down of the pipe coupling, the respective ends of the respective coupling segments flex inwardly and are caused to move towards each other, in order to move the teeth at the ends of the coupling segments into biting engagement with the pipe exterior, the only other option being to relieve the teeth at the opposite ends of the coupling segment in a direction tangential to the radius of the coupling.
Segmented pipe couplings are known in which one end of the traction bolt is pivotally secured within the bolting pads of one of the coupling segments, and which can be swung into a position in which the nuts can be engaged with the bolting pads of the next adjacent coupling segment. Such a construction is disclosed in Stillwagon U.S. Pat. No. 2,459,251 issued Jan. 18, 1949, which, while intended for use with metal piping, also would find use in the coupling of high-density polyurethane piping.
In that construction, the ends of the bolts are pivotally mounted within the bolting pads of the associated coupling segment by providing hinge pins that extend through the bolt heads, and which are secured within the associated bolting pads.
In that construction, while the traction bolts and the bolting pads can hinge relative to each other, no provision is made for corresponding movement of the bolts relative to the bolting pads of the next adjacent coupling segment. Thus, in the event that the bolting face of the next adjacent coupling segment is not truly perpendicular to the axis of the shank of the bolt, but is inclined thereto, the nut will engage the bolting face of the associated bolting pad in essentially line contact extending radially of the bolt axis, i.e., the nuts will not be in continuous end face engagement with the bolting face of the bolting pad. This gives rise to the tensional forces existing in the bolt acting in a direction that is other than co-axial with the shank of the bolt, and which results in bending or attempted bending of the shank of the bolt.
Further problems arise as a result of the nut attempting to spiral along the associated bolting face as the nut is torqued down to the required value. However, at that time, the nut is attempting to bite into the associated bolting face at the location of line engagement, a circumstance which again militates against the nut reaching true parallelism with the associated bolting face.
The result is that under mechanical or thermal loading of the assembled pipes and segmented pipe coupling, the nut can move relative to its associated bolting face, and, it will attempt to do so in order to bring the operative face of the nut into continuous face engagement with the associated bolting face. This movement of the nut in an attempt to reach parallelism with the bolting face will result in a reduction in the tensile stress in the shank of the bolt, and in turn will result in a reduction in the clamping force exerted by the segmented pipe coupling on the associated pipes.
The positioning of a washer under the nut in no way removes this problem, in that the washer, during torquing down of the nut, becomes engaged with the associated bolting face with a very considerable resistance to movement of the washer relative to the bolting face.
It is also known to provide T-bolts in which the head of the bolt is integral with the shank instead of being pivotally interconnected with the shank. Such a construction is disclosed in Skelly U.S. Pat. No. 2,837,383 issued Jun. 3, 1958.
While the bolt of this reference overcomes the inherent requirement of providing a pivot pin at the bolt head, as is essential to the Stillwagon construction, the teachings of Skelly are not directly related to the employment of the Skelly construction in a segmented pipe coupling. While Skelly teaches a T-bolt having an integral head, a nut applied to the shank of the bolt, and a saddle that is capable of rotation relative to its supporting member, Skelly also requires that the saddle be channelled for it to extend around one half of the circumference of the bolt shank, which can result in the trunnions of the saddle moving out of axial alignment with one another under the effects of tensional loading of the shank of the bolt. This problem in Skelly is of little consequence in Skelly""s construction, which, as previously mentioned, bears little relationship to the environment of a segmented pipe coupling.
In another form of coupling, as taught by U.S. Pat. No. 4,611,839, the adjacent ends of the respective coupling segments are intentionally required to move axially relative to each other in opposite directions during the torquing down of the traction bolts, in order to provide a segmented pipe coupling capable of maximizing the rigidity of the coupling when it is in a fully assembled condition.
Each of the above circumstances give rise to totally unexpected and uncontrollable conditions, and can result in a reduction of the tensile stress present in the traction bolts.
This is due to numerous variable conditions which arise during assembly of the coupling and during use of the coupling. Such variables arise when the shank of the bolt is unable to reach a condition in which its axis is truly perpendicular to the bolting faces of both of the bolting pads. In that event, maximum pressure will be exerted at one location circumferentially of the head of the traction bolt than is exerted at other locations around the circumference of the bolt head. If maximum pressure is exerted at one position on the bolt head, then a force will be present acting to move the head itself into a position in which it is other than perpendicular to the axis of the shank of the bolt, with an attempted ripping-off of the bolt head, and, which in turn resolves itself as bending or bowing of the shank of the traction bolt.
This problem is further exaggerated in the event that the nut does not extend in perfectly parallel relation relative to the bolting face of the opposite bolting pad, a condition which seldom occurs, and, which is not achievable in the event that the shank of the traction bolt has a bowed due to the conditions arising at the head of the bolt.
Further, the existence of extremely localized and extremely high pressures at a point on the circumference of the bolt head can result in the bolt head bedding down and becoming matrixed at that location into the somewhat rough surface of the as-cast bolting face. This, in turn, militates against the bolt head sliding relative to its associated bolting face into true parallelism with the associated bolting face.
The same condition arises at the nut, and at the washer in the event that a washer is employed, i.e., the localized extremely high pressures militate against the nut or the washer reorienting themselves in true parallelism with the associated bolting face.
In the event that a washer is not employed, then, a further problem arises. Unless the operative face of the nut is exactly in parallelism with its associated bolting face, and invariably it is not in such a position, the nut will attempt to spiral across the associated bolting face. That condition further acts to move the shank of the bolt out of its perpendicular relation to the oppositely presented bolting faces, further increasing the possibility of bowing of the shank of the nut, and acting even further to move the operative face of the nut out of parallelism with the associated bolting face.
Other variations can occur arising from manufacturing tolerances in the traction bolt and its associated nut, and, manufacturing tolerances in the coupling segments themselves arising from the casting process employed in the manufacture of the coupling segments.
Upon torquing down of the nut to the desired value, a positive indication will be given that the traction bolt is properly and fully torqued down to the intended value. At the immediate time the torque value is initially established, possibly this is so. However, the presence of so many variables can later result in the torque value being significantly reduced. If the traction bolt moves from the initial position at which the required torque value was obtained to another position, then, the tensile stress in the shank of the bolt can become reduced. This can happen due to mechanical loading exerted on the associated pipes, or thermal working due to temperature variations in the pipes and in the couplings, or due to cold working of the metal comprising the bolt head and the associated nut, and, in extreme circumstances can arise from angling of the bolt head relative to the bolt shank for the operative face of the bolt head to become other than truly perpendicular to the longitudinal axis of the bolt shank.
A further problem that can occur with conventional traction bolts is that the end of the shank of the traction bolt can move laterally within the bolt hole of the associated bolting pad to a position in which the shank, and probably the threaded portion of the shank is forced into engagement with the side wall of the bolt hole, particularly in the vicinity of the nut. If this happens, then a resultant error occurs in the value to which the nut is torqued down onto the associated bolting face. This is due to the fact that frictional engagement then exists between the shank of the bolt and the associated wall of the associated bolting head, which can cause scuffing and abrasion of the side wall of the bolt hole or of the shank of the bolt, particularly in view of the fact that the shank of the bolt and the bolting head of the associated coupling segment are moving relative to each other during the closing down of the bolting heads of the respective coupling segments. Having obtained an accurate, but in fact, false reading of the torque value, subsequent movement of the traction bolt relative to the bolt hole of the associated bolting pad can result in the frictional engagement disappearing, at which point the value to which the nut is torqued down correspondingly decreases.
Additional variations in the value to which the traction bolt is torqued down can arise due to crushing-down of the surface of the as-cast bolting pads, as an alternative to cold-working of the bolt head or the associated face of the associated nut. While that condition cannot be eliminated in its entirety, it is significantly reduced in the event that the forces exerted between the traction bolts and the respective bolting pads can be equalized to the greatest possible extent.
Any reduction in the extent to which the traction bolt is torqued down then can result in a reduction in the force with which the respective coupling segments engage the associated pipes or fittings, thus resulting in the coupling exhibiting reduced capability in providing a truly rigid coupling.
It is an object of this invention to provide a traction bolt that will eliminate or significantly reduce the problems resulting from use of conventional traction bolts.
It is a further object of this invention to provide a segmented pipe coupling employing traction bolts, that can predictably maintain the clamping pressure to which it is initially subjected, and, in which the desired clamping pressure is substantially unaffected by conditions that occur subsequent to the clamping down of the respective coupling segments.
It is a further object of this invention to provide a traction bolt in which the stresses exerted in the shank of the traction bolt predictably are tensile stresses acting in parallelism with the longitudinal axis of the shank of the traction bolt, thus to militate against bowing of the shank of the traction bolt under the applied traction forces.
It is a further object of this invention to reduce or eliminate the consequences of spiralling of the nut relative to its associated bolting face, and, the consequences of scuffing, abrasion, and frictional resistance resulting from relative movement between the shank of the traction bolt and the associated wall of the bolt hole of the associated bolting pad.
It is a further object of this invention to eliminate the effects of movements of the bolting faces of the respective bolting pads towards or out of parallelism with one another during torqueing down of the coupling segments of the segmented pipe coupling.
It is another object of this invention to provide a segmented pipe coupling in which the extent of torqueing down of the respective traction bolts, and the clamping pressures exerted by the respective coupling segments, can predictably be maintained in the presence of mechanical or thermal stresses applied to the assembled segmented pipe coupling.
It is also an object of this invention to provide a segmented pipe coupling and traction bolt assembly, in which the traction bolt is subjected exclusively to tensional forces extending parallel to the axis of the bolt shank, and which thus will accommodate situations in which the respective bolting faces are other than truly perpendicular to the longitudinal axis of the coupling segment.
According to the present invention, the segmented pipe coupling and T-bolt combination provides a seating for the head of the T-bolt, which permits rotary movement of the T-bolt about the longitudinal axis of the head of the T-bolt, the head of the T-bolt being formed as a cylinder or knife edge.
The mutually presented bolting head of the next adjacent segmented pipe coupling is provided with bolt holes of a diameter larger than the diameter of the bolt shank, in order that the bolt shank is free to move within the bolt holes by swinging about the longitudinal axis of the head of the T-bolt.
In this manner, when the nut is applied to the shank of the T-bolt, the nut automatically will come into complete face engagement with the bolting face of its associated bolting pad, the T-bolt being free to rotate about the longitudinal axis of the bolt head. In this manner, it is assured that bending forces in the shank of the bolt are eliminated, and, that the operative face of the bolt reaches continuous face engagement with the face of the associated bolting pad, despite the probability that the respective bolting faces are not in true parallelism with each other and extending a truly paralleled to a radial plane that includes the longitudinal axis of the coupling segment.
According to another embodiment of the present invention, a T-bolt having a head integral with the shank of the bolt is pivotally supported in one of the bolting pads, and a yoke-shaped saddle is positioned on the shank of the bolt, and which can move axially of the bolt. The saddle is held in position by a nut which engages the saddle, the saddle being formed in a similar manner to the head of the traction bolt in order that it can pivot relative to the bolting pad of the next adjacent coupling segment.
By this construction, tensional forces applied to the shank of the bolt automatically act to rotate the head of the T-bolt and the saddle relative to their associated bolting pads, in order to ensure that the nut engages the face of the saddle in continuous face engagement as opposed to line-engagement, thus to relieve the shank of any bending forces developed in the shank.
By virtue of the capability of the nut to engage the saddle in continuous face engagement and the ability of the head of the T-bolt to rotate relative to its associated bolting pad, there is no possibility of the nut engaging the saddle in line-engagement, and in turn, there is no possibility of the nut moving relative to the saddle under mechanical or thermal loading, thus to provide a traction bolt for a segmented pipe coupling that predictably can be torqued down to the required extent, and in which the tensional loading of the bolt shank predictably will be maintained in the presence of mechanical or thermal working of the segmented pipe coupling and the associated pipes to which it is applied.